In the modern aircraft construction industry, skin sheets made of “laminate sheets” (known as “GLARE®”) are widely used for covering the fuselage. Such skin sheets are produced by layering thin aluminium sheets, which are adhesively bonded to one another with an adhesive layer, on top of one another. Each adhesive layer comprises at least one resin-impregnated, unidirectional fibreglass insert for mechanical reinforcement.
The entire laminate sheet construction, consisting of alternate layers of aluminium alloy sheets layered on top of one another and adhesive layers therebetween, is cured by using pressure and temperature in an autoclave or in a heatable press to form a laminate sheet. These laminate sheets are processed further in the same way as conventional aluminium alloy sheets. The adhesive layers, which ensure the cohesion between the aluminium alloy sheets, are preferably formed with fibreglass inserts which are impregnated or saturated with a curable epoxy resin and are each up to 0.5 mm thick. The aluminium alloy sheets are also up to 0.5 mm thick. The adhesive layers may also each comprise at least two fibreglass inserts with differing fibre flow directions. Alternatively, other types of fibre inserts (for example carbon fibres or aramide fibres) may be used in combination with other plastics materials such as polyester, BMI resins or thermoplastic polymers to form the adhesive layers.
Adhesively bonding the laminate layers together produces a mechanically highly loadable, plate-shaped laminate sheet which is highly resistant to fatigue and has a low crack propagation rate. In addition, the laminate sheet is characterised by a high resistance to impact.
At least two shell portions produced using laminate sheets of this type are generally connected along at least two longitudinal seams to produce the approximately barrel-shaped fuselage sections. Manufacturing half shells or quarter shells is conventional in fuselage shell production. Connecting the shell portions is generally carried out using the known riveting method or by forming overlapping longitudinal seams or butt welds with connecting butt straps arranged at the interior. A plurality of fuselage frame sections is subsequently connected by forming circumferential transverse seams to form a complete aircraft fuselage section.
Welding the laminate sheets, which is considerably less costly in comparison to the conventional riveting method, has not been possible up to now since the fibreglass inserts of the laminate sheets would contaminate the weld and, in addition, the high thermal load in the region of the weld may lead to delamination of the laminate sheet. Both of these effects result in a considerable reduction in the mechanical load-bearing capacity of the produced longitudinal seams.